Light Emitting Diodes (“LEDs”) have several advantages for outdoor lighting over High Intensity Discharge (“HID”) light sources, such as long life, lower energy consumption, durability, cold weather performance, directional orientation of beam patterns, instant on/off and controlled dimming without color change. In particular, the directional nature of the LED light gives the ability to create asymmetric light beam emission patterns by orienting and directing multiple LED light engines within the fixture, rather than relying solely upon reflectors and focusing lenses as in conventional light sources.
A major concern, however, when designing an LED outdoor fixture, is effective heat management. Heat at the semiconductor domain junctions is a primary determinant in the lifetime of the LED and in maintaining consistent wavelength. LEDs function better and last longer at cold or cool temperatures, and deteriorate more rapidly with increased heat. The design effort to draw heat away from the junctions has often resulted in the LED circuit boards being attached to a finned heat sink, with natural air convection or fans used for cooling. In an outdoor light fixture, however, the ambient temperature may at times be relatively high even at night, there may be little natural air movement in or around the fixture, and little ventilation from within the fixture. Hence, convection heat transfer is limited, and developing a different solution to heat management is a design criteria.
In addition to the utilitarian design considerations, outdoor pole and wall mounted luminaries are often decorative pieces, mimicking ornate gas lanterns and early incandescent street and park lighting. Some of the most ornate are cast metal housings that incorporate the architectural design elements of the locale or historical periods. Replacing the light source in such fixtures with LED lighting is a particularly challenging task, and one that is addressed in this invention.